Status and Rank of the Tertiary and Quaternary

9-13-06

The KGS Stratigraphic Nomenclature Committee looks to the International Commission on Stratigraphy (ICS) for guidance concerning era/erathem, period/system, epoch/series, and age/stage level nomenclature designations as they apply to Kansas. The status and rank of the terms Tertiary and Quaternary have been debated for over 100 years without resolution; however, the ICS's current formal position is that the Tertiary and Quaternary are sub-era/sub-erathem in rank and Paleogene and Neogene have period/system rank. The Tertiary-Quaternary boundary is placed at the base of the Gelasian Age/Stage (~2.6 Ma), the uppermost age/stage of the Pliocene Epoch/Series (see ICS's chart at http://www.stratigraphy.org/cheu.pdf, PDF file). The debate continues, but a final decision is expected in the next 2-3 years.

The Kansas Geological Survey has adopted the ICS's current position on Cenozoic nomenclature and will use this scheme (fig. 1) in its publications until the issue has been resolved.

Figure 1. Kansas Geological Survey's current position on the rank and status of the Cenozoic in Kansas.

Background

Giovanni Arduino (1759) proposed that geologic time be divided into three orders: the Primary, Secondary, and Tertiary. The Primary and Secondary--terms that have long been obsolete--were approximately equal to today's Paleozoic and Mesozoic Eras/Erathems. Only the term Tertiary has survived.

Jules Desnoyers (1829) proposed the term Quaternary to describe deposits that were younger than the Tertiary rocks as they were known at that time. Since then, the Quaternary has generally been used to describe the Earth's most recent cycle of glacial and interglacial activity, including the occurrence of humans and modern processes. However, the boundary between the Tertiary and Quaternary has never been formally defined, making these terms inappropriate for formal scientific use (the beginning of the Tertiary is defined by the end of the Cretaceous and the Quaternary continues to the modern day, but where the Tertiary ends and the Quaternary begins is still in dispute [Rohde, 2005]).

As part of its attempt to standardize the geologic time scale (a task to be completed by 2008), the International Commission on Stratigraphy (ICS) did away with the terms Tertiary and Quaternary, gave Paleogene (Naumann, 1866) and Neogene (Hörnes, 1853) Period/System rank, and extended the Neogene to include the Pleistocene and Holocene (Berggren et al., 1995; Berggren, 1998; Gradstein et al., 2004 [see chart at http://earth-time.org/chus.pdf, PDF file]; and others). While this solution avoids the Tertiary/Quaternary boundary debate and provides a clear definition for scientific use, it overlooks a long history and tradition of usage.

Activity Since Publication of A Geologic Time Scale 2004

The decision to abandon the term Tertiary follows the historical trend that abandoned Primary and Secondary, and the scientific community has apparently accepted this change (Ogg, 2004; Aubry, 2005). The term Quaternary, however, has received overwhelming support to be retained as a formal chronostratigraphic unit. Following publication of A Geologic Time Scale 2004 (Gradstein et al., 2004), the ICS and the International Union for Quaternary Research (INQUA) formed the Quaternary Task Group to define the Quaternary in a stratigraphic sense and make it part of the international time scale. The Task Group's recommendations (see http://www.stratigraphy.org/Q2.pdf, PDF file) were presented to the full ICS voting membership (consisting of the executive officers of the ICS and the chairs of the ICS subcommissions), and the recommendations resulting from that vote were announced on September 28, 2005 (see http://www.stratigraphy.org/Q1.pdf, PDF file). Their recommendations regarding the definition and rank of the Quaternary were:

The Quaternary is to be recognized as a formally defined and ratified geochronologic/chronostratigraphic subdivision of the Cenozoic Era/Erathem.

The Quaternary spans the past ~2.6 million years of the Cenozoic, and its formal base will coincide with the basal Global Stratotype Section and Point (GSSP) of the Gelasian Age/Stage of the Pliocene Epoch/Series.

The Quaternary will have the rank of sub-era/sub-erathem in the geologic time scale and is coeval with the uppermost portion of the Neogene Period/System.

The ICS's recommendations were submitted to INQUA for their formal acceptance before the ICS requested formal ratification from the International Union of Geological Sciences (IUGS). In their November 2005, newsletter (http://www.inqua.tcd.ie/documents/QP%2015-2.pdf, PDF file, INQUA requested comments from their membership on these recommendations.

In a letter to the ICS dated March 24, 2006 (subsequently published in the INQUA newsletter; see http://www.inqua.tcd.ie/documents/QP%2016-1.pdf, PDF file), INQUA rejected the ICS proposal. While INQUA supported the recommendations to recognize the Quaternary as a formal chronostratigraphic unit and to define the base of the Quaternary at the base of the Gelasian Age/Stage (~2.6 Ma), it rejected the rank of sub-era/sub-erathem for the Quaternary (INQUA considers the rank of period/system essential) and wants to lower the base of the Pleistocene (from ~1.8 Ma) to ~2.6 Ma to coincide with the "Quaternary Period/System" boundary.

Current Status

ICS's response to INQUA in a letter dated July 20, 2006 (go to the Subcommission on Quaternary Stratigraphy page at http://www.quaternary.stratigraphy.org.uk/meetings/task.html and scroll down to "ICS response to the formal position of INQUA--August 2006" and click the icon) summarized "the only two aspects that INQUA and ICS are not currently in complete agreement are: (1) rank of Quaternary, and (2) whether the long-established Pleistocene should also be extended downward". The ICS's proposed course of action during the next 2-3 years will be:

The ICS will continue to display Quaternary as spanning the past 2.6 Ma on its official posted time scales (http://www.stratigraphy.org/cheu.pdf) and show an informal Tertiary sub-era below the Quaternary, but indicate the lack of an IUGS-IGC (International Union of Geological Sciences--International Geological Congress) ratification.

INQUA will discuss further the basal definition of the Quaternary, the implications of proposing to extend the Pleistocene to include the Gelasian stage, and strive to enhance global and regional correlation methods for reliably correlating the base-Gelasian in non-magnetostratigraphic sections. INQUA will then make a corresponding request to IUGS and ICS. As in 1998, it is probable that a joint task group will be assigned to evaluate the scientific rationale for redefining the Pleistocene.

If IUGS-IGC ratifies the downward extension of the Pleistocene, then INQUA can request to instate the Quaternary as a new period in the geologic time scale above the Neogene Period.